An optical pick-up device is generally driven electromagnetically to place the device's objective lens at a desired location along an optical disc, in focusing and tracking directions. For focusing, an optical pick-up actuator serves to move the objective lens to maintain its desired relative position to the disc. For tracking, an optical pick-up device traces tracks of the disk in order to record information on the disk or read information recorded on the disc. In an optical recording/reproducing system for recording and reproducing information, an objective lens is actuated to allow an optical spot to follow the surface vibrations and eccentricity of a disk in order to achieve the desired focusing and tracking operations.
For most optical pick-up devices, a widely used two-axis actuator includes a moving part which conducts macroscopic translational motions for focusing and tracking. The moving part should be actuated without generating unnecessary vibrations in order to reduce optical signal errors. The tilt of the optical disk caused by the deflection and mechanical run-out of the optical disc, increases coma aberration, which is critical in systems with a large numerical aperture. Thus, tilt compensation is strongly required for recording and reproduction systems. However, it is difficult for a two-axis optical pick-up actuator to compensate for coma aberration. Moreover, there is a sub-resonance problem due to mass unbalance or nonlinearlty of the moving parts.
In order to solve those problems, optical pick-up devices used in recording/reproducing systems require three-axis macroscopic mechanical motions for focusing, tracking and tilt compensation. Such a device is described in U.S. Patent No. 2004/0052180 A1. However, three-axis actuators have many other disadvantages, including, but not limited to, their complicated structure, large volume, heavy weight, low speed, high cost, and weakness for vibration.
Recently, the needs for high-density, high-speed, and miniaturization have been increased, and there has been much work to develop technologies to satisfy these needs. A high-density optical disc has been developed to have high capacity. The size of the laser beam focused onto the disc should be reduced to record information on such a high-density disk or to read the recorded information. In order to record and/or read the information on/from the high-density disk, a laser with a reduced wavelength and an objective lens with a large numerical aperture have been used. In addition, other technologies such as multi-layered recording, near-field optical recording, hologram, and so on have been developed to increase the capacity on a data storage media.
Further, technologies, hologram and multi-beam optical pick-up, have been developed for high-speed reproduction. But, these technologies are not practical yet. In addition to the need for high capacity, there is a growing need for small and thin size. However, it is very difficult to satisfy the requirements for high-speed and/or miniaturization with conventional servo technology.
Thus, there is a practical need for an optical pick-up device that provides focusing, tracking, and tilt compensation with minimal macroscopic motion. This device must be able to withstand vibration and satisfy the needs for high-speed, miniaturization, and low production cost.